The disposal of organic waste materials such as sewage sludge, animal manure, food processing waste, and the like, presents both environment and public health concerns.
The production of large volumes of sludge as an end-product from wastewater treatment processes poses one of the biggest challenges to the wastewater treatment industry. The handling and disposal of sludge residuals has significant social, environmental, and economic implications. Treatment and disposal of sewage sludge from wastewater treatment plants can account for over half of the total cost of wastewater treatment plant construction and operation. Currently, residual sludge is commonly digested, incinerated, deposited in landfills, or used as fertilizer through agricultural land application of the residual biosolids.
In current wastewater treatment processes, toxic heavy metals become concentrated in the residual sludge. There may also be dangerous levels pathogenic organisms present in the residuals. For these reasons there are increasing concerns that land application of sludge residuals may be harmful to the environment and to public health. Under such social, environmental and economic pressures, significant effort has been invested in developing new methods of treating wastewater and wastewater sludges that result in smaller amounts of residual requiring disposal.
Anaerobic digestion is a very common solids reduction and stabilization technology, but is relatively inefficient due to the low biodegradability of the sludge. This poor biodegradability is particularly evident in the case of digesting secondary or waste activated sludge. The benefit of anaerobic digestion is that the methanogenesis stage of the process results in the production of methane (biogas) which can be used as an energy source. To improve the efficiency of the anaerobic digestion process, many techniques which enhance the biodegradability of these sludges have been developed in recent years.
The anaerobic degradation of particulate organics is considered to be a sequence of three steps: hydrolysis, acidogenesis, and methanogenesis. Among these, biological hydrolysis of the particulate organics has been considered to be the rate limiting step.
Many of the techniques recently developed to improve the biodegradability of sludges therefore focus on improving hydrolysis by other means. The processes most focused on are chemical oxidation disintegration by ozone, mechanical disintegration by various methods, and thermal or thermal/chemical disintegration. These techniques include those discussed in the following references:                Ahn, K.-H., Park, K. Y., Maeng, S. K., Hwang, J. H., Lee, J. W., Song, K. G. and Choi, S. (2002). Ozonation of wastewater and ozonation for recycling. Wat. Sci. Tech., 46(10), 71-77.        Chiu, Y. C., Chang, C. N., Lim, J. G. and Huang, S. J. (1997). Alkaline and ultrasonic pre-treatment of sludge before anaerobic digestion. Wat. Sci. Tech., 36(11), 155-162.        Hiraoka, M., Takeda, N., Sakai, S. and Yasuda, A. (1984). Highly efficient anaerobic digestion with thermal pre-treatment. Wat. Sci. Tech., 17(4/5), 529-539.        Kepp, U., Machenbach, I., Weisz, N. and Solheim, O. E. (2000). Enhanced stabilisation of sewage sludge through thermal hydrolysis—three years experience with full scale plant. Wat. Sci. Tech., 42(9), 89-96.        Recktenwald, M. and Karlsson, I. (2003). Recovery of wastewater sludge components by acid hydrolysis. Presented at IWA Specialised Conf. BIOSOLIDS 2003 Wastewater Sludge as a Resource, Trondheim, Norway, 23-25 Jun. 2003.        Svanström, M., Modell, M. and Tester, J. (2004). Direct energy recovery from primary and secondary sludges by supercritical water oxidation. Wat. Sci. Tech., 49(10), 201-208.        Tiehm, A., Nickel, K., Zellhorn, M. and Neis, U. (2001). Ultrasonic waste activated sludge disintegration for improving anaerobic stabilization. Water Research, 35, 2003-2009.        Weisz, N., Kepp, U., Norli, M., Panter, K. and Solheim, O. E. (2000). Sludge disintegration with thermal hydrolysis—cases from Norway, Denmark and United Kingdom. 1st IWA World Congress, Paris 3-7 July. Pre-prints Book 4, pp 288-295.        Yasui, H. and Shibata, M. (1994). An innovative approach to reduce excess sludge production in the activated sludge process. Wat. Sci. Tech., 30(9), 11-20.        
Most of these prior processes operate either with large amount of chemical dosage or under high temperature and pressure conditions or both. Energy consumptions are typically large for many of these processes.
There remains a need for a cost-effective process to achieve solid waste disintegration, nutrient solubilization and pathogen destruction.
The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.